Dear Cornelius, I agree with you that it's better to prepare for the exam using a device with a bigger screen, closer to what we will use in the real exam.
However, being able to use transport time or any idle time away from a computer to practice, is really helpful. I'm with Mohammad

With that said: I tried several times to access the simulator with my smartphone (Android 9 with Chrome browser) without luck.
The dropdown menu on the right side of the home page seams to just flash and disapear in mobile Chrome.
But I have found a workaround: I just access the simulator in my desktop and send that link to my phone. It works perfectly.
I hope it helps.
Best regards!